High pressure compact arc discharge lamp for multiphase operation

ABSTRACT

A high pressure compact arc discharge lamp with an inert gas filling and which is combined with a reflector, includes three co-planar equivalent principal electrodes for multiphase operation. The electrode tips are located to form corners of an isosceles triangle lying within the discharge space of the lamp and are located at the center of curvature of the reflector which projects the discharge space. The upper electrode is vertically oriented and the spacing of the tips from one another is matched to the dimensions of the area to be illuminated (e.g. an image aperture). The discharge currents between the electrodes are directly connected.

United States Patent [191 Schlegel [451 Oct. 16, 1973 HIGH PRESSURE COMPACT ARC DISCHARGE LAMP FOR MULTIPHASE OPERATION [75] Inventor: Horst Schlegel, Soecking, Germany [21] Appl. No.: 168,926

[30] Foreign Application Priority Data Oct. 8, 1970 Germany P 20 49 524.3

[56] References Cited UNITED STATES PATENTS 2,459,516 1/1949 Francis et a1. 313/188 3-PHASE to pin 11 POWER to pin 12 SOURCE to pin 13 2,673,944 3/1954 Francis 313/184 X 2,153,036 4/1939 Burt et 31.. 315/147 X 2,966,607 12/1960 Thouret 313/113 2,974,249 3/1961 Thouret.... 315/334 X 2,945,146 7/1960 Meyer 313/113 3,090,883 5/1963 Bauer 313/113 Primary Examiner-Pa1mer C. Demeo Attorney-Robert D. Flynn et al.

[5 7] ABSTRACT A high pressure compact arc discharge lamp with an inert gas filling and which is combined with a reflector, includes three co-planar equivalent principal electrodes for multiphase operation. The electrode tips are located to form corners of an isosceles triangle lying within the discharge space of the lamp and are located at the center of curvature of the reflector which projects the discharge space. The upper electrode isVertically oriented and the spacing of the tips from one another is matched to the dimensions of the area to be illuminated (e.g. an image aperture). The discharge currents between the electrodes are directly connected.

PATENIEUncr 16 I975 3-PHASE to pin 11 POWER to pin 12 SOURCE to pin 13 INVENTOR Horst Schlegel IIIGH PRESSURE COMPACT ARC DISCHARGE LAMP FOR MULTIPHASE OPERATION This invention relates to a high pressure compact arc discharge lamp for multiphase operation, and more particularly to such a lamp which includes more than two principal electrodes and which is combined with a reflector. The present lamp is particularly useful for projection purposes.

Lamps with more than two principal electrodes are known in the art, In most cases, these lamps are high pressure mercury lamps, either being provided with additional auxiliary electrodes (U.S. Pat. No. 2,153,036), or being provided with a stellate discharge vessel with the electrodes extending only a short length into the ends of the individual arms of the discharge vessel, and having great arc lengths (Czechoslovakian Pat. No. 127,210). The lamps known per se are operated from direct or alternating current with a possibly added heterodyne modulated direct or alternating current (German Pat. No. 685,096, corresponding to British Pat. No. 506,690). Alternatively, they are operated from multiphase current (U.S. Pat. No. 2,116,702); in this case, however, the circuits are not directly connected. As a rule, the number of electrodes is even and they are substantially operating in pairs.

Since identical power rating high pressure lamps with a filling of mercury require lower currents than high pressure lamps with an inert gas filling, the preferred utilization of mercury lamps suggested itself to those skilled in the art. As is well known, higher currents result in more extensive electrode destruction during use.

The use of high pressure discharge lamps with an inert gas filling, namely lamps of higher wattage ratings, seems however desirable for special fields of application. Such increase in wattage could be obtained by increasing the voltage or by spacing the electrodes a greater distance apart. A voltage increase implies however an increase in pressure. Since the pressure in these lamps is generally already approaching the safety limit, this method cannot be applied. A larger spacing of the electrodes, on the other hand, leads to a reduced stability of the arc and to a decrease in luminance, whereby the lamp is rendered less suited for projection purposes.

It is the aim of the present invention to provide a high pressure compact arc discharge lamp with inert gas filling which is of compact structure and may be operated with increased wattage rating without a substantially increased discharge current, and which displays high uniform luminance across a larger area.

SUMMARY OF THE INVENTION The high pressure compact arc discharge lamp for multiphase operation according to the present invention, which is combined with a reflector and which has more than two principal electrodes, is characterized in that the lamp includes an inert gas filling and comprises three equivalent principal electrodes which are disposed in a common plane perpendicular to the direction of light emission of the lamp such that straight lines connecting the electrode tips are within the discharge space of the lamp, and that the electrode tips form corners of an isosceles triangle lying at the center of curvature of the reflector which projects the area of discharge. One of the electrodes is so disposed as to extend upwards and perpendicular to the direction of emission. The location of the electrode tips at the corners of an isosceles triangle includes, of course, also the location of the electrode tips at the corners of an equilateral triangle.

The vertical position of one of the electrodes ensures that the arc struck between the two other electrodes is not upwardly deflected. When mounting the electrodes with their tips forming the comers of an isosceles triangle, the top electrode is for reasons of symmetry, the one which is facing the base of the triangle. Due to the conformal projection of the electrodes when using a spherical reflector yielding a wrong-sided image which is turned upside down, the triangular arrangement of the electrode tips optically becomes a rectangular arrangement. With a suitable selection of the spacings between the individual electrode tips, said rectangle of the area to be illuminated may be matched, for example, to the size of the image aperture of a projector. Preferably both the reflector and the lamp form a single structural unit.

BRIEF DESCRIPTION OF THE DRAWINGS In FIG. 1, the electrodes 1, 2 and 3 of thoriated tungsten which are displaced by 120 from one another, are

introduced respectively across the molybdenum foil seals 4, 5 and 6 into the discharge vessel 7 of quartz glass which has an outer diameter of 25 mm. The bases 8, 9 and 10 are provided respectively with contact pins 11, 12 and 13. The electrodes 1, 2 and 3 are arranged so that their respective electrode tips l4, l5 and 16 form the corners of an isosceles triangle, the length of the base of the triangle being 2 mm and that of its other legs 1.7 mm each. The radius of the spherical reflector 17 of polished aluminum is approx. 30 mm. The discharge vessel 7 contains xenon at a fill pressure exceeding 10 atmospheres. The lamp is connected, via contact pins 11, 12 and 13, to a three-phase generator source 18 having a terminal voltage of 3 X volts. The lamp current per.phase is 10 amps. The are voltage between two electrodes is 14 volts. The lamp has a power input of 250 watts and a power factor of 0.99. The operating frequency is approx. 600 cycles. The lamp has a luminous intensity of 530 candels.

A direct connection of the three electrodes to a three-phase generator or to the three-phase mains is eventually established across circuit elements. The power source 18 shown in FIG. 1 includes all such circuit elements. This means that the discharge currents between the electrodes are directly connected. The three electrodes are equvalent insofar as a main discharge arc forms from each electrode to any of the other electrodes.

In FIG. 2, like parts are denoted by the same reference numerals. The reflector 17 projects an image 1' of electrode 1 opposite to the electrode.

, The lamp of the present invention may be operated from an audio-frequency power source. When using the lamp in film projectors, the frequency preferably exceeds 200 Hz. Thus operation is feasible, for example, from a slightly modified, commercially available three-phase electric generator for motor vehicles, adapted to work at 600 Hz. This is of advantage in nonstationary film projection systems. Operation of the lamp from higher frequencies results in reduction of electrode destruction. Of course, the lamp may be used also in headlights possibly without a reflector combined therewith.

The lamp combined with a reflector according to the present invention unites high wattage rating with a good color rendition which is due to the continuous, having a spectral distribution resembling solar radiation. In spite of the increased wattage rating, compared with a high pressure xenon lamp comprising only two electrodes, the useful life of the present lamp is not shorter because of the practically identical current load. Moreover, the uniform illumination matched to the image aperture, is of great advantage for film projection. The present lamp gives high uniform luminance over a larger surface area. Due to its immediate readiness for service, the lamp is also particularly suited, for instance, for microscropy.

I claim: 1. An electric compact arc discharge lamp for threephase operation comprising three terminal means (11, 12, 13) to connect the lamp to a three-phase source (18);

a sealed, transparent envelope (7);

an ionizable inert gas atmosphere at high pressure within the envelope (7);

and three spaced similar principal electrodes (1, 2, 3) connected to the three terminal means located within the envelope (7) and having spaced end tips (14, 15, 16) to effect a short discharge are between the tips, said three electrodes (1, 2, 3) being located in a common plane which is perpendicularto the direction of light emission of the lamp to provide an arc occurring essentially in said common plane, said electrodes being placed with respect to each other such that the end tips (14, l5, 16) of the electrodes form corners of an isosceles triangle, and being placed within the envelope such that the tips of the electrodes, located at the corners of said triangle are spaced by a smaller distance from another than from the envelope wall and that the end tips, defining said isoceles triangle are essentially at the center of the envelope;

one (1) of said electrodes (1, 2, 3) extending upwardly with respect to said direction of light emission.

2. Lamp according to claim 1 wherein said electrode (1) extending vertically upwardly and perpendicularly to said direction of light emission faces the base of said isosceles triangle formed by said eledtrode tips (14, 15, 16).

3. Lamp according to claim 1, adapted to illuminate a rectangular area, in combination with a reversing reflector l7 located adjacent the envelope, wherein the spacing of the tips (14, 15, 16) of said electrodes from one another and the reflector is such that upon reversal of the image of the isoceles triangle which is formed by said electrode tips (14, 15, 16) due to the reversing reflector, an area of illumination will be provided which is essentially rectangular.

4. Lamp according to claim 3, wherein both said reflector (l7) and the lamp are formed as a single structural unit.

5. The combination of claim 1, wherein the frequency of the source is in the audio frequency range.

6. The combination of claim 1, wherein the frequency of the source exceeds 200 Hz.

7. The combination of claim 6, wherein said frequency is approximately 600 Hz.

8. An arc lamp and reflector combination for threephase operation comprising a sealed transparent envelope (7);

a reversing reflector (17) located adjacent the envelope; three spaced similar principal electrodes (1, 2, 3) having spaced end tips (14, 15, 16) located within the envelope (7);

three terminal means (11, 12, 13) connected to the electrodes to connect the lamp to a three-phase source (18);

an ionizable inert gas atmosphere at high pressure within the envelope (7);

the three principal electrodes (1, 2, 3) being located in a common plane which is perpendicular to the direction of light emission'of the lamp to provide an are occurring essentially in said common plane, said electrodes being placed with respect to each other such that the end tips (14, 15, 16) of the electrodes form corners of an isosceles triangle so that the arc will be a short discharge arc occurring between the tips, the isosceles triangle having two equal sides and a base, the electrodes being further placed within the envelope such that the tips of the electrodes, located at the corners of said triangle, are spaced by a smaller distance from another than from the envelope wall, the end tips defining said isosceles triangle being located at the center of curvature of the reflector, the electrode facing the base of the isosceles triangle, formed by said electrode tip, extending upwardly and perpendicularly to said direction of light emission, the relative location of said common plane in which the electrodes, defining the isosceles triangle are placed, being spaced from said reversing reflector such that, upon reversal of the image of the isosceles triangle formed by the electrode tips, an area of illumination will be provided which is essentially rectangular and has two opposite sides defined essentially by the base of said isosceles triangle. 

1. An electric compact arc discharge lamp for three-phase operation comprising three terminal means (11, 12, 13) to connect the lamp to a three-phase source (18); a sealed, transparent envelope (7); an ionizable inert gas atmosphere at high pressure within the envelope (7); and three spaced similar principal electrodes (1, 2, 3) connected to the three terminal means located within the envelope (7) and having spaced end tips (14, 15, 16) to effect a short discharge arc between the tips, said three electrodes (1, 2, 3) being located in a common plane which is perpendicular to the direction of light emission of the lamp to provide an arc occurring essentially in said common plane, said electrodes being placed with respect to each other such that the end tips (14, 15, 16) of the electrodes form corners of an isosceles triangle, and being placed within the envelope such that the tips of the electrodes, located at the corners of said triangle are spaced by a smaller distance from another than from the envelope wall and that the end tips, defining said isosceles triangle are essentially at the center of the envelope; one (1) of said electrodes (1, 2, 3) extending upwardly with respect to said direction of light emission.
 2. Lamp according to claim 1 wherein said electrode (1) extending vertically upwardly and perpendicularly to said direction of light emission faces the base of said isosceles triangle formed by said electrode tips (14, 15, 16).
 3. Lamp according to claim 1, adapted to illuminate a rectangular area, in combination with a reversing reflector (17) located adjacent the envelope, wherein the spacing of the tips (14, 15, 16) of said electrodes from one another and the reflector is such that upon reversal of the image of the isoceles triangle which is formed by said electrode tips (14, 15, 16) due to the reversing reflector, an area of illumination will be provided which is essentially rectangular.
 4. Lamp according to claim 3, wherein both said reflector (17) and the lamp are formed as a single structural unit.
 5. The combination of claim 1, wherein the frequency of the source is in the audio frequency range.
 6. The combination of claim 1, wherein the frequency of the source exceeds 200 Hz.
 7. The combination of claim 6, wherein said frequency is approximately 600 Hz.
 8. An arc lamp and reflector combination for three-phase operation comprising a sealed transparent envelope (7); a reversing reflector (17) located adjacent the envelope; three spaced similar principal electrodes (1, 2, 3) having spaced end tips (14, 15, 16) located within the envelope (7); three terminal means (11, 12, 13) connected to the electrodes to connect the lamp to a three-phase source (18); an ionizaBle inert gas atmosphere at high pressure within the envelope (7); the three principal electrodes (1, 2, 3) being located in a common plane which is perpendicular to the direction of light emission of the lamp to provide an arc occurring essentially in said common plane, said electrodes being placed with respect to each other such that the end tips (14, 15, 16) of the electrodes form corners of an isosceles triangle so that the arc will be a short discharge arc occurring between the tips, the isosceles triangle having two equal sides and a base, the electrodes being further placed within the envelope such that the tips of the electrodes, located at the corners of said triangle, are spaced by a smaller distance from another than from the envelope wall, the end tips defining said isosceles triangle being located at the center of curvature of the reflector, the electrode facing the base of the isosceles triangle, formed by said electrode tip, extending upwardly and perpendicularly to said direction of light emission, the relative location of said common plane in which the electrodes, defining the isosceles triangle are placed, being spaced from said reversing reflector such that, upon reversal of the image of the isosceles triangle formed by the electrode tips, an area of illumination will be provided which is essentially rectangular and has two opposite sides defined essentially by the base of said isosceles triangle. 